U.S. Pat. No. 3,504,457 is directed to a composite or multi-layer pad which includes a foam polyurethane polishing layer, an intermediate porous layer, and a nitrile rubber layer. However, this type of pad generally does not uniformly planarize the substrate being polished.
The pad of this invention preferably comprises a relatively soft layer with a porous structure, preferably microporous, wherein the soft layer is impregnated with a relatively hard material. Under polishing pressures, the relatively hard material preferably deforms locally and irreversibly to a substantially flat polishing pad surface resulting in a polished substrate surface with relatively high planarity and substantially low form error. In an embodiment, the soft layer comprises a polymeric material having a glass transition temperature up to about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50xc2x0 C., and the hard material comprises a polymeric material having a glass transition temperature in a range of about 25xc2x0 C. to about 175xc2x0 C. including 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, or 175xc2x0 C. In an embodiment, the porous structure is self-supporting or in the alternative is coated onto a substrate, preferably flexible.